readme: Update download link for SDK to 1.10.1

Closes #566

README.md

@@ -22,7 +22,7 @@ Installing Panda3D
 ==================
 
 The latest Panda3D SDK can be downloaded from
-[this page](https://www.panda3d.org/download/sdk-1-10-0/).
+[this page](https://www.panda3d.org/download/sdk-1-10-1/).
 If you are familiar with installing Python packages, you can use
 the following comand: